What alternative health

practitioners might not tell you



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"Table 3 has the smoking gun..…My conclusion, from reading the paper in its entirety, rather than the abstract, is that a population that should not have a stroke, the young, has a marked increase association with stroke 24 hours after visiting a chiropractor…..In real medicine, it takes less data than this to bring a drug under scrutiny to decide if the benefits are worth the potential risks of a therapy." Evaluation by Mark Crislip, MD, Science Based Medicine (17th July 2008)

The evaluation also notes the following regarding neck manipulation force: “…in a good hanging, the victim should not strangle to death (1). A good hanging should be set up such that there is a fall just far enough so that the first and second vertebral bodies are separated, breaking the neck and quickly killing the victim. You do not want them to fall too far, as the head may come clean off and that is aesthetically unpleasant. Most people who die these days from hanging do not get a ‘good’ hanging; they suffocate at the end of a rope, a particularly gruesome way to die. The vertebral artery is often damaged in suicidal hanging (2); “The vertebral artery was shown to be injured quite frequently (rupture, intimal tear, sub-intimal hemorrhage), namely in one quarter of all cases, and indeed in more than half taking into account the perivascular bleeding.” This easy injury is in part due to mechanical reasons “The vertebral arteries appear to be particularly susceptible to injury in trauma of the cervical spine because of their close anatomical relationship to the spine” (3). A passive hanging (no drop) gives about 686 Newton’s of force around the neck for a 70 kg human. In chiropractic, “the mean force of all manual applications (is) 264 Newton’s and the mean force duration (is) 145 milliseconds (8)”. So a chiropractic neck manipulation, for a short period of time, can provide 38% the force of a hanging. And a bad hanging at that."

FULL TEXT of the Cassidy paper [pdf]

PREFACE: Neck Pain and the Decade of the Bone and Joint 2000–2010

FULL TEXT of all papers contained in Neck Pain and the Decade of the Bone and Joint 2000–2010



I have a copy of the paper. If I am interpreting it correctly, a figure that stands out is that patients with VAD who are <45 are 12 times more likely than non-VAD persons to have attended a chiropractor within the previous 24 hours 95% CI (1.25-115.36). For chiropractic attendance within three days the figure is 3.33 (1.02-10.92), and the association remains up to 30 days Odds ratio 3.13 (1.48-6.63). There is NO such association for the over 45 age group -- 0.55 (0.16-1.85) for having seen a chiropractor within 24 hours.

This in accord with what the observational evidence suggests --- strokes coming on immediately, or within a day or so after neck manipulation in young persons.

The big "however", and the only new thing that the Cassidy paper contributes, is that there is at least an equally strong association with doctor attendances -- here there is an Odds ratio of 11.21 (3.59-35.03) for 0-1 days and 9.53 (3.96-22.97) for 0-3 days. And, interestingly, there does remain a strong association of VAD with doctor visits in the previous 24 hours with an OR of 6.65 (4.18-10.58) in the over 45s.

What can it all mean? I have always accepted that some patients may have attended a chiropractor because of neck pain that is actually due to a stroke in progress, but this is definitely NOT an adequate answer for all cases. Many have had no preceding relevant symptoms, or have been treated for more chronic complaints.

May the answer lie in a source of bias that is not considered in the paper's discussion? I have little personal experience in neurology but I suspect that most patients with early VAD will also have worrying neurological symptoms and that this draws the majority of patients with VAD towards medical doctors rather than chiropractors for any medical attendances that occur prior to hospital admission.

And medical attendances is all that is being measured here. It is not a direct assessment of the effects of neck manipulation.


The study itself did not report the presenting complaint or whether neck manipulation was performed, so it was really meaningless. What if patients with early stroke symptoms are more likely to see a medical doctor than a chiropractor and what if some of the patients had no pre-existing symptoms but saw a chiropractor for health maintenance and had strokes as a result? The data would look the same. The author's speculation that patients who saw chiropractors were already having a stroke is in no way supported by the data. And of course, chiropractors seeing a patient with stroke symptoms should have recognized them and sent the patient to a hospital. If they can't recognize stroke symptoms, they are likely doing neck manipulations on these already vulnerable patients, which can't be good.

The really pitiful thing is that chiropractors could so easily keep a register of presenting complaints, type of manipulations, and follow-ups to see if stroke was later diagnosed. If they kept good records, they could either SHOW us that there was no association between neck manipulation and stroke, or they could show that there was a tiny risk and they could have quantified it and maybe figured out which patients were at greatest risk. If a similar risk was even remotely suspected for a scientific medical treatment, you can bet physicians would have done that kind of research by now.

We have plenty of smoking gun cases where a patient with no headache or neck pain got neck manipulation and collapsed on the table with torn vertebral arteries. Chiropractors would have us believe that they would have collapsed anyway without manipulation, but they can't offer any supporting data. The very fact that they try to defend these cases with rationalizations and speculations rather than data just shows how far they are from science-based thinking.


Cassidy was very adamant in pointing out, entirely correctly, that a statistical association does not equal causality…One might have wanted to ask about the "association" between peoples' recovering health after a visit to the chiropractor and primary care physician, respectively. I mean, they do base their whole so-called profession on the faith in causality between chiropractic "care" and beneficial health outcomes, don't they?

DCs like to "point out" that all reports of adverse effects of chiropractic, including stroke and death, are only "case reports" and "anecdotes" and thus meaningless, because there are no control groups. They seem to have learnt the lesson from the critique by the medical science side that anecdotes don't count as data. But they are missing the whole thing, the difference between an experimental study and reports of adverse effects, that aren't of course experimental and can't have control groups. I have never heard of a real medical doctor dismissing any "anecdotic" reports of adverse effects of drugs or other medical treatments -- and neither do the DCs in that context!! On the contrary, they almost always end up in tu quoque arguments against NSAIDs in their pathetic attempts at justifying chiropractic.

This stubborn denial of any possible inkling of a thought of a suspicion of causality between neck manipulation and the frequent smoke-gun-reported adverse effects is a terrible disgrace to Cassidy and the chiropractors as fellow human beings as well as professional health care providers. But I think I understand them, because -- please tell me if I am correct or incorrect in believing this -- that if they admitted that there might be an ever-so-small causal relationship between neck manipulation and stroke, they would risk lots of litigation processes where they would lose and have to pay huge amounts of money to the victims? That might explain why they so strongly object to even having a form for written consent, since such a piece of paper would count as admitting the risk, or?

The only really interesting piece of information is that Cassidy has conceded that he once had a patient who got a stroke on his manipulation table after neck manipulation. Cassidy did think, at the time, that the manipulation caused the stroke, but that he does not think so now any more, thanks to his study. This opens up for the suspicion that he was heavily biased in architecting the study...Unlike most medical articles nowadays, the Cassidy report has no "Disclosure statement" or "Declaration of potential bias". Maybe purposely omitted?

When a stroke occurs in a chiropractor's office during or immediately following a neck manipulation, especially in the case of a healthy young person, there is good reason to suspect a temporal or causative association with neck manipulation. In many cases, however, a stroke caused by neck manipulation may occur days later when a damaged vertebral or carotid artery releases a blood clot or an embolus that travels to the brain stem or to the brain. When these patients develop symptoms of stroke, they will go to the emergency room or seek medical care rather than go to a chiropractor’s office. The patient may not report the neck manipulation he or she had at the chiropractor’s office and the physician may be unaware that the patient had such treatment (most often for conditions or reasons other than head or neck pain), thus relieving the chiropractor of any blame and jacking up the number of stroke victims seeking primary care. For this reason, it may be misleading to say that the incidence of stroke associated with chiropractic care is the same as that associated with primary care, as reported in the Cassidy study.


One of my greatest concerns is that they seem *not* to have included those who died or otherwise were not *discharged*. They do not even mention them, so we do not know the number of exclusions. The text is not clear on this matter (except that recently dead persons or long-term care residents were excluded from the *controls*). I may be seriously wrong on this issue, because I don't understand exactly what "discharge abstract" is in this context…I learned that Canada has specially trained "abstractors", but nobody asked if they were medically trained persons or clerical staff, or what.


The Cassidy study confirmed previous findings of an association between vertebrobasilar artery stroke and chiropractic visits in those under 45 years of age.

The odds ratio for PCPs is a separate issue and we don’t know what it means. The assumption that patients sought care for pre-existing symptoms of stroke was not justified by the data. The data collection method did not permit any conclusions about that or even about neck manipulation.

So far no study has directly assessed the relationship between presenting symptoms, neck manipulation vs. other interventions, and stroke. That is the kind of study we need. Chiropractors themselves have been concerned about the stroke/neck manipulation connection, but they haven’t yet studied it in any meaningful way.

In the recent hearings in Connecticut Cassidy testified that he had once thought he was responsible for a stroke that his patient suffered after neck manipulation, but he changed his mind after the Cassidy study. I don’t think he was justified in changing his mind based on those inadequate data.

What we really want to know is whether neck manipulation is a risk factor for stroke. The data from several studies, the many “smoking gun” case histories, and the presence of a credible mechanism suggest that it is. If previous visits with PCPs are associated with stroke, that is an entirely separate question. If pre-existing neck pain predicts these strokes and prompts visits to any provider, that would be useful to know, but this study doesn’t illuminate us. The study didn’t even address neck manipulation, only visits to chiropractors – which might have involved activator or other treatments without manipulation. And for all we know, a few of the visits to PCPs could have involved neck manipulation, particularly if the PCP was a DO.

The study may serve a psychological function for chiropractors by reinforcing their beliefs but it is really useless as far as helping us understand what is going on. It certainly does not show that neck manipulation can’t cause strokes. I think most chiropractors would hesitate to manipulate the neck of someone who was having a stroke in progress; and if there is no reliable way to differentiate those patients from patients with musculoskeletal neck pain, doesn’t that mean that chiropractors ought to be reluctant to manipulate any patient with neck pain?